Manufacture of wood pulp, etc.



Patented den. 26, 1932 UNITED STATES PATENT (OFFICE.

lLINN BRADLEY, F MDNTCLAIR, NEW JERSEY, AND EDWARD P. MOKEEFE, OF NEWYORK, N. Y.

MANUFACTURE OI WOOD PULP, ETC.

N0 llrawing. Application filed June 28,

This invention relates to improvements in the production of pulp fromWood and similar cellulose-bearing materials.

The common methods of producing wood pulp chemically, are the so-calledsoda, sulfate and sulfite'processes. In the so-called soda process, themain cooking operation is dependent upon caustic soda. In the socalledsulfate process the main cooking operw ation is dependent upon causticsoda assisted more or less by sodium sulfide, although some sodiumcarbonate and sodium sulfate may be present. in the so-called sulfiteprocess the main cooking operation depends upon bisul- M tites in thepresence of sulfurous acid. In the soda and sulfate processes,accordingly, the cooking liquor is strongly alkaline, while in thesulfite process the cooking liquor is strongly acid; and it has beenconsidered immy practical to cook wood successfully, for the productionof chemical pulp, unless the cooking liquor was either strongly acid orstrongly alkaline.

in all three of the processes mentioned, the as cooking liquors employedact not only upon the encrusting and so-called non-celluloseconstituents or'so-called lignin or lignified tissues of thewood, butalso to a greater or less extent upon the cellulose or pulp mak 3o ingfibres, and usually destroy or injure a considerable portion of thevaluable fibres or' cellulose, or convert an appreciable portion thereofinto constituents which are removed from the pulp. Sometimes theresidual liquors from the process are also of such a character that theyleave in the pulp constituents which make the pulp difficult to bleach"with the usual bleaching materials and operations, so that the fibresmaybe still further 40 injured by the severe bleaching treatment whichit is necessary to employ.

The rapidly decreasing supply of woods suitable and availablefor pulpmaking purposes and the high cost of equipment and R operation ofchemical pulp mills makes it of 1921. Serial No. 481,146.

great national and economic importance to materially increase the yieldof pulp from woods which are commonly used for the purtained by chemicalmethodsof disintegrating wood, even those now employed, is far superiorin quality, including strength, to that obtained by the ground Woodprocess, and a much wider range of woods canbe used.

As the result of our investigations, we have been impressed with thefact that a considerable portion of the pulp content of the wood treatedwas not being recovered in the form of pulp, and We have thereforestudied the cooking processes with the View of determining whether anincreased yield of pulp could be obtained-from the same amount of woodby other methods than those heretofore employed.

We have found that if, instead of a strongly acid or strongly alkalinecooking liquor, the cooking liquor is neutral in character or is onlyweakly alkaline, an increased yield of a superior pulp can be, obtained.We have studied the effect of various cooking liquors and varioustreatments upon different kinds of wood and have determined that theingredients associated with the Wood fibres may generally be consideredas consisting of two kinds, namely, constituents readily re1novable fromthe fibres by a mild reagent in the presence of water at a suitabletemperature and pressure, and other constituents which are lessreadilyremovable by mild reagents but which are readily removable withstrong 7 tion upon the fibres.

ably near the end of the cook. Tn any event, however, the amount ofcaustic soda required will be small, and will be insufficient in amountto have objectionable action upon the fibres so that the pulp producedwill contain" substantially all of the fibres originally pres ent in thewood, freed from non-fibrous con- I soluble in the amount of liquor usedshould be suitably circulated so as to keep the undissolved reagent insuspension and fairly uniformly distributed. This avoids the productionof acidic liquors in localized zones.

The cooking operation may also be carried out with less of the reagentsthan will completely cook the wood, and a partially cooked orunder-cooked woodpulp produced. For eirample. sodium sulfite alone canbe used under conditions such that the wood is partially cooked, and thecooking operation can then be followed by a mechanical treatment oranother chemical treatment to further prepare the wood pulp forsubsequent treatment or use.

Tn the treatment of certain woods by the use of a strong reagent such ascaustic alkali in addition to the mild reagent, to produce a well-cookedwood pulp, the cooking operation may advantageously be divided into twosteps or stages. The first part of the operation can thus he carried outwith a mild. reagent or reagents either alone or with a small amount ofa strong reagent, and the second part of the cooking operation can becarried out with a strong reagent, either alone or with amild reagent.For example, by using sodium sulfite alone for the preliminary part ofthe cook and by then adding a small amount of caustic soda andcompleting the operation, the caustic soda will not have op portunity toact upon the wood until it has been disintegrated to a considerableextent by the sodium sulfite. A better opportunity is thus afforded forthe action of the sodium sulfite upon the wood, and this action issupplemented by the subsequent portion of the cook carried out withadded caustic soda. This enables a lesser amount of caustic soda to beused, as it is not present during the entire cooking operation. So also,it acts upon the wood chips for a shorter period of time, thus lesseningthe possibility of injurious ac- A particularly advantageous method ofcarrying out the two-stage cook above described is to introduce, forexample, suitable sodium sulfite cooking liquor, into the sodium sulfitecooking llquor, to introduce a suiiicient amount of lime to causticize apart of the sodium snlfite. That is, by introducing a small andregulated amount of lime into the digester, the lime'will react with thesodium sulfite to form caustic sodaand calcium sulfite, so that. thecooking liquor will thereafter contain both sodium sulfite and causticsoda together with calcium sulfite. The lime is preferably introduced inthe form of screened milk of lime and the reaction is brought about bythe circulation which takes place within the digester. The caustic sodais thus produced within the digester as needed.

Instead of carrying out the process as a two stage cook, by adding themilk'of lime ing operation 50 that a mixture of sodium sulfite andcaustic soda will be formed in this way at the outsetof the process; orthe lime may be added in stages as the cooking operation proceedsthusprogressively producing sodium hydroxide in the cooking liquor.

If the calcium sulfite or other calcium compounds are objectionable inthe pulp, they can be removed therefrom, for example, by. washing thepulp with a dilute acid such as sulfurous acid inwater after the pulphas been removed from the digester. Where the presence of calciumcompounds is unobjectionable in the pulp, for example, the presence ofcalcium sulfate or gypsum, the pulp can be treated with dilute sulfuricacid or a solution of sodium bisulfate to form calcium sulfate and setfree any organic acids, etc., with which the calcium is combined. Thecalcium sulfate may be left in the pulp as a filler, and where theorganic compounds are suitable, they may also be left inthe pulp assizing or binding materials.

By using neutral or weakly alkaline reacting liquors, the process can becarried out in iron vessels, so,that linings such as are now.

used in the so-"called sulfite process can be dispensed with, withresulting increased capacity of the digester. The digester can also becharged with hot liquors, and the digester can be l filled as'full aspracticable with the wood \khips. The cooking liquors are sufiicientlyii -gt in their action upon the valuable fibres st that chips can becooked for different peifods of time in the same charge without 0'ject-ionable injury due to overcooking of part of the charge. As aresult, a partof the charge can be introduced and the cooking operationcommenced so that the charge can be compacted in the digester and afurther amount of chips introduced so that the char e as a Whole can bematerially increased. For example, the

When a multi-stage cook is used and one liquor is removed beforeintroducing another, the digester may be opened at a suit-- able time,such as between the successive stages, and advantage taken of the factthat the wood chips already partially cooked, have packed considerably,thus leaving a considerable amount of available space which can befilled with additional wood chips which will be subjected to thesuccessive portions of the cooking operation. An additional amount ofwood chips can be treated in this way in the same apparatus. Wherediiferent cooking liquors are employed in successive stages [of thecook, the residual liquors obtained will vary in character from eachother.

When the two stage cook is carried out with a sodium sulfite cookingliquor, the liquors may smilarly be withdrawn at the end of thesuccessive stages. For example, resinous pine woods may be cooked at atemperature corresponding to about 120 pounds saturated steam pressurefor about four or five hours with a solution containing an ex-.

cess of sodium sulfite, and the residual liquor can then be removed fromthe fiber-bearing material and the fiber-bearing material then cookedfor a further period'of, for example,

four hours at the same temperature and steam pressure and with asolution containing a suitable amount of caustic soda, insuflicient toinjure the fibres to any objectionable extent, but suflicient to removeresinous and tained in this way in relatively large amount similarnon-fibrous constituents not. removed by the sodium sulfite. The finalliquor will be relatively more saponaceous due to the presence of resinsoap. This soap' can be ohand made available for use as a soap ingre- 9client or for sizing or other purposes. When normal sodium sulfite aloneis used in excess during the early portion of the cook, its actionaccordingly is more or less selective in that only a part of theresinous constituents are attacked and removed, so' that such con-ystituents as reinain can be later removed by the dilute caustic sodatreatment, but without the necessity for'using more than a small amountof caustic soda which is insulficient toserlously injure the fibres. a

It is one advantage of the present invention that indirect heating ofthe digester'can be employed in a particularly advantageous manner,inasmuch as the cooking liquor is either neutral or mildly alkaline, sothat it has no objectionable corroding action such as results from theuse of acid liquors. The residual liquors produced, as well as thecooking liquors during the cooking operation, have less organic matterin solution than the liquors of the usual pulp processes, if the sameamount of liquor is employed, and the organic matter partakes of asomewhat different character and is less liable to deposit on the tubesor coils of a heater or heat exchanger. So, also, pumps can more readilybe operated to circulate the liquor against the high pressures and atthe high temperatures employed, where the liquor is neutral or weaklyalkaline than where the liquor is either strongly acid or stronglyalkaline.

We have also found that it is not necessary to keep the chips submergedduring the cooking operations, provided the chips are properly subjectedto the action of the cooking liquor by employing suitable circulationfor example, by spreading the cooking liquor at the tops of the digesterand allowing it to penetrate down around or through the chips to beagain returned to the top and recirculated. This method of procedurepermits the employment of a lesser quantity of cooking liquor, withsaving in the amount of liquor to be pumped and in the heat required forheating the body of liquor, as well as in evaporation and other recoverysteps owing to the lesser amount of residual liquor to hanliquor to becirculated can be varied by introducing additional liquor of a differentcharacter, so that it will be introduced into the digester along withthe other li uor that is being circulated. When the co g operation hasreached a desired point, for example, the liquor can be changed so thatthe subsequent portion of the cook will have a modified cooking liquor.The liquor used in one cooking operation or in a preliminary portion ofthe cook may even be drawn off and circulated through another digester,thus further carrying out the selective treatment of different chargesof chips in different digesters, or utilizing the same liquor fortreating successive charges in different digesters.

It will accordingly be seen that the present invention provides aprocess of producing wood pulp from wood in which both strong acid andstrong alkali cooking liquors are avoided, and in which a neutral orweakly al-' agents for effecting-the major portion of the cookingoperation, either alone or together with a strong reagent in small andregulated It will also be seen that the present process utilizes a mildreagent or reamount, either with the mild reagent or alone, and eitherin a single or multi-stage cooking operation, so as to insure theseparation of the fibres from the associated ingredients to such anextent as to form a suitable pulp. By using the mild and strong reagentsin this way, it is possible to reduce the amount of the strong reagentto a minimum such that it has no seriously objectionable action upon thefibres of the wood treated.

Tn the claims the term acid in the phrase to prevent the cooking liquorfrom becoming acid refers to the use of litm-us as the indicator.

l. The method of treating wood so as to produce wood pulp, whichcomprises subjecting the wood to a cooking operation under pressure andat an elevated temperature with a cooking liquor utilizing a mildcooking reagent and thereafter changing the composition of the cookingliquor by the addition of an alkali and completing the cook with saidchanged liquor.

2. The method of treating wood so as to produce wood pulp, whichcomprises subjecting the wood to a cooking operation under pressure andat an elevated temperature with a cooking liquor utilizing a mildcooking reagent and thereafter changing the composition of the cookingliquor by the addition of a reagent or reagents without completereduction of the pressure within the cooking apparatus.

8. The method of treating wood so as to produce wood pulp, whichcomprises subjecting the wood to a cooking operation under pressure andat an elevated temperature with a cooking liquor utilizing a mildcooking reagent and thereafter changing the composition of the cookingliquor by the addition of a reagent or reagents without greatly reducingthe temperature and pressure within the cooking apparatus, andthereafter completing the cooking operation.

at. The method of treating wood chips which comprises subjecting thechips to a partial cooking operation with one cooking liquor andcompleting the cooking operation with a cooking liquor of modifiedcomposi-,

'tion, the cooking liquor being circulated and controlled so that thechips are cooked by percolation without the chips being completelysubmerged, the cooking liquor being maintained neutral or alkaline andbeing prevented from becoming acid during the cooking operation.

5. The method of treating wood for the production of wood pulp therefromwhich comprises subjecting the wood to a partial cooking operation underpressure and at an elevated temperature with a neutral or mildlyalkaline cooking liquor containing monosultite to give a partiallycooked product, and subjecting the partially cooked product to a furtherchemical treatment to prepare wood pulp therefrom.

6. The method of treating wood for the production of wood pulp therefromwhich comprises subjecting the wood to a partial ment to prepare woodpulp therefrom.

7. The method of treating wood for the production of wood pulp therefromwhich comprises subjecting the wood to a partial cooking operation underpressure and at an elevated temperature with a sodium monosulfitecooking liquor, to give a partially cooked product, and subjecting thepartially cooked product to a further chemical treatment to prepare woodpulp therefrom.

8. The method of treating wood for the production of wood pulp therefromwhich comprises subjecting the wood to a partial cooking operation underpressure andat an elevated temperature with a sodium monosulfite cookingliquor to give (a partially cooked product, the cookin operation beingwill completely cook the wood, and subjecting the partially cookedproduct to a further chemical treatment to prepare wood pulp therefrom.

9. The method of treating wood so as to produce wood pulp whichcomprises subjecting the wood to a cooking operation under pressure andat an elevated temperature with a neutral or mildly alkaline cookingliquor and thereafter changing the composition of the cooking liquorcontaining monosulfite by the addition of an alkali. I

10. The method of treating wood chips which comprises subjecting thechips to a partial cooking operation with a neutral or mildly alkalinecooking liquorand completing carried out with less of the, reagents thanthe cooking operation with a cooking liquor having alkali therein, thecooking liquor being circulated and controlled so that the chips arecooked by percolation without the chips being completely submerged.

11. The method of treating wood for the production of pulp whichcomprises treating the wood at an elevated temperature with a cookingliquor containing undissolved reagents in suspension, the volume ofwhich is less than would submerge the entire mass of wood andcirculating the liquor so that any undissolved reagents will be kept insuspension therein and all the wood will be subjected thereto.

12. The method of treating wood chips which comprises subjecting thechips to a partial cooking operation with cooking liquors insufficientto submerge the chips, circulating the liquor in such manner thattheliquor is distributed evenly over the top of the mass of chips and iscaused to percolate down through the mass, changing the chem icalcomposition of the liquor by adding chemicals to the liquor during thecirculation and completing the cook with the modified liquor.

13. The method of separating resins from wood with the simultaneousproduction of' pulp and resin soaps which comprises par tially cookingthe wood in a liquor containing a mild reagent having a selective actionon a part of the non-cellulose, withdrawing the liquor whensubstantially all the non- .cellulose materials, except the resins, havebeen dissolved, completing the cook with a an alkaline residual liquorcontaining dissolved matter derived in part from such firstmentionedorganic matter; (0) subsequently washing fibres derived from the saidmaterial treated in step a.

' .17. The process according to claim 16, wherein the amount of sulfiteused in step atis insuflicient to convert wood into chemical pulp.

In testimony whereof we aifix our signatures.

LINN BRADLEY.

- EDWARD P. KcKEEFE.

caustic alkali and recovering resin soap fronf lulose-containingmaterial, by means of aliquor maintained alkaline, so as to reduce thepercentage of non-cellulose therein and obtain at the termination ofsuch latter treatment an alkaline residual liquor containing dissolvedmatter derived in part from such first-mentioned organic matter; (a)subsequently washing fibres derived from the sai material treated instep a.

15. The process according to claim 14 wherein the amount of digestingmaterial used in step a is insuflicient to convert wood into chemicalpulp.

16. The process of treating fibre-bearing material which comprises thefollowing steps: (a) subjecting fibre-bearing material containingcellulose and other undissolved organic matter of wood origin to adigesting treatment so as to solubilize a substantial portion of thesaid organic matter by means of a sulfite; (b) subsequently supplying tofibre-bearing material, derived from the said material mentioned instepa and containing undissolved organic matter including cellulose, an alkaline reagent which is capable oiwofibih'zing a substantialportion ofsuch organic matter, and treating the cellulose-containing material, bymeans of a liquor maintained alkaline, so as to reduce the percentage ofnon-cellulose therein and obtain at the termination of such lattertreatment iao

